Methods and apparatus for automotive tire inflation with air are known. Examples are found in U.S. Pat. Nos. 4,333,491; 4,456,038; 4,702,287; 4,782,878; 5,611,875; and 5,891,277.
In known methods and apparatus for automotive tire inflation with air, where tires are simultaneously filled with air, typically, all four tires are filled simultaneously from a single air source. Valve stems at the tire are typically very imprecise devices. Access to the interior of a tire is restricted, to a varying degree, based on the relative position of the valve core in the valve stem and the valve core depressor on the filling device. A problem that can occur is that the tires may not all be equally pressurized as a result of the varying valve stem restrictions.
The advantages of using nitrogen rather than air for tire inflation for improved safety, longer tire life, and therefore less cost, have been recognized. Apparatus and methods to intermittently manufacture and dispense nitrogen for use in product manufacturing processes or for tire inflation have been proposed in U.S. Pat. Nos. 5,588,984; 5,688,306; and 5,855,646, for example. In these known apparatus, compressed air enters a nitrogen module containing a permeable membrane that selectively separates nitrogen from the air and discharges oxygen and other gases. The nitrogen gas then flows into a vessel for storage. In U.S. Pat. No. 5,588,984, a means for vending the nitrogen gas from the apparatus allows customers to financially activate the apparatus to obtain a desired amount of nitrogen gas which can be dispensed to a tire to be filled by way of flexible hoses and an air chuck. There is a need for an improved method and apparatus for filling tires with nitrogen in an accurate and efficient manner and which enable simultaneous filling of all four tires of a vehicle so that they are equally pressurized with high purity nitrogen.